Consider the reaction PCl5 (g) PCl3 (g) + Cl2 (g) in a closed container at equilibrium. At a fixed temperature what will be the effect of adding more PCl5 on the equilibrium concentration of Cl2 (g) ?

According to Le-Chatelier's principle, when the reactant 5 PCl is added in the reaction, then the reaction is favoured in the forward direction which results in the increase in the concentration of the product i.e. 2 Cl .